Corrosion inhibitor



of metals, such as the cooling systems of internal Patented Feb. 26, 1935 UNITED STATE CORROSION INHIBITOR Henry L. Cox, Charleston, W. Va., aaaignor to .Carbide and Carbon Chemicals Corporation, a

corporation .of New York No Drawing.

Application November Serial No. 495,302

3 Claims. (01. zsz---s) This invention relates to the prevention of metal corrosion. induced by the presence of certain liquids. The invention is especially applicable to coolingsystems which are constructed combustion engines which employ water, alcohols, or water solutions of alcohols for the circulating liquid, but it may be applied to other liquid systems which are subject to corrosion.

Various alcohols in solution with water are used in the cooling systems of internal combustion engines, and in certain instances alcohols alone may beused for this purpose. My invention is especially applicable to prevent the oxi-' dizing action of such cooling media. The term alcohol as used in. this specification and the appended claims, includes all the liquid saturated aliphatic hydroxy compounds. The compounds of this class which have been used extensively are the mono-hydroxy alcohols, such as metha nol, ethanol, propanol, and the poly-hydroxy alcohols such as ethylene glycol, diethylene glycol, propylene glycol and glycerol.

Corrosion of the metallic parts of liquid systems, such as those portions comprising iron, copper, brass or solder, commonly results in a lowered efliciency of the system. Corrosion roughens the heating and cooling surfaces, and produces sediment and sludge which impair the heat transferring functions of the systems. Excessive corrosion causes-leaking which necessitates repair or replacement of the damaged parts. The use of substantially non-corrosive liquids, such as pure water, is impracticable since it is usually impossible to prevent contamination of the liquids by adventitious additions of gases, and other corrosion producing substances to which the liquids are exposed. It is furthermore desirable that the non-corrosive liquid employed should be stable, free from disagreeable odors, and free from objectionable color or stain producing properties.

One of the objects of my invention is to provide means for rendering and maintaining liquid media substantially non-corrosive to metals.

Another object of my invention is to provide an apparatus for the dissipation of heat in which the metal portions shall be substantially free from corrosion.

Cooling media containing additions of a hydroxy-alkylamine, such as triethanolamine, have been found satisfactory in inhibiting corrosion in respect to iron and certain related metals and alloys. However, such additions may render the media unduly corrosive toward metals and alloys which are attacked under alkaline conditions. I have found that this difliculty may be avoided by partially or wholly neutralizing the hydroxy-alkylamine by means of an acid. The acid used may be an inorganic acid such as phosphoric acid, or .an organic acid such as oleic, palmitic or stearic acid. It may be added as such, or in the case of the organic acid, it may be supplied in the form of lard oil or similar glycerides containing free fatty acids.

These salts of hydroxy-alkylamines either with or without the presence of the free bydroxy-alkylamine, have been found to be very eillcient as inhibitors of corrosion in liquid systems.

The following examples are illustrative of my invention: 1

I. A cooling system composed mainly of iron was operated with water in which 0.25% by weight of triethanolamine was dissolved. The corrosion produced in this system was found to be only about seven ,thousandths as much as that produced by water alone, under the same conditions of operation.

. II. A cooling system composed mainly of iron, 25 was operated with water in which 1.0 by weight of triethanolamine phosphate was dissolved. In this casethe corrosion produced was too slight to be determinedJThis composition was found to be nearly equally advantageous when used in cooling systems comprisingother metals and alloys, namely, brass, copper and solder.

III. A cooling system'composed mainly of iron was operated with water to which was added 0.25% by weight of triethanolamine partially neutralized with 0.5% by weight of lard oil containing about 10% 15% free fatty acid.- As in Example II, this composition was used in systems composed of other metals, and in all cases reduced corrosion to negligible proportions.

IV. Cooling, systems like those described in Example 11 were operated with a water solution of an alcohol containing 1.0% by weight of triethanolamine phosphate. The corrosion produced wasnegligible as compared to that produced by a solution containing only water and alcohol.

An alcohol solution containing 0.25% by weight of triethanolamine, and 0.5% by weight of lard oil gave 'very similar results.

V. Cooling systems like those described in Example II were operated with an alcohol as the cooling medium, with about 0.33% by weight of triethanolamine in the alcohol; with about 1.5% by weight of triethanolamine phosphate in the 55 alcohol; and with about 0.75% by weight of triethanolamine neutralized in part with about 1.5%

by weight of lard oil added to the alcohol. With the above additions, the corrosion produced in each case was negligible, as compared to that produced by the alcohol alone.

Mono or diethanolamine, mixtures of mono-, diand triethanolamine, or other hydroxy-alkylamines, such as propanolamine, etc., may be used instead of triethanolamine. Salts of inorganic and organic acids, such as the borates, acetates, formates and oxalates of hydroxy-alkylamines may be used instead of the phosphate, or the hydroxy-alkylamine may be partially or wholly neutralized with a fatty acid, such as stearic acid, oleic acid, palmitic acid, or mixtures of fatty acids, such as those found in lard oil and similar organic oils.

In each instance the result of the added inhibitor is to produce and maintain conditions in the solution which will render the liquid less corroslve to metal. Since an acidic condition is, in the main, the most prevalent in untreated liquids that are corrosive, the inhibitor added is in each case alkaline. The hydroxy-alkylamine whenused alone, neutralizes the undesirable acidity, but as has been stated, excessive alkalinity is undesirable, and somewhat more beneficial results are produced by partially neutralizing the alkaline hydroxy-alkylamine with an acid. It is necessary to use an acid which will form stable salts with the hydroxy-alkylamine, such salts being inert in respect to the liquid used, and producing a wholly stable condition in the final solution.

If the hydroxy-alkylamine is to be neutralized or partly neutralized by-means of lard oil or similar glycerides, excess amounts may be used inasmuch as the presence of the oil or the glycerides will not cause injurious corrosion in the system.

The concentration of the inhibitor in the liquid is dependent upon the liquid to be treated, the inhibitor to be used and the metals of which the liquid system is formed. The limits of concentration may, however, be determined by well knowntests. Thus, it has been determined that in a 35% solution by volume of ethylene glycol in water, the most satisfactory limits of concentration which will produce non-corrosive solutions are as follows:

1 Per cent 'Iriethanolamine 0.10 to 0.35 Triethanolamine phosphate 0.25 to 1.0

'Iriethanolamine lard oil 0.15 to 0.75 and 0.5 to

1.5 respectively. The above proportions refer to percent by weight of the composition.

:1 claim:

1. A liquid cooling medium for use in conjunction with a metal radiator, comprising an alcohol and a salt of an acid of the group consisting of oleic, palmitic and stearic and an ethanolamine,

said salt being present in suflicient quantity to inhibit the corrosion of said radiator.

HENRY L. COX. 

